Automatic telephone system



Nov. 5, 1940. N. E. NlLssoN 2,220,423

AUTOMATIC TELEPHONE SYSTEM Filed Sept. 27, 1937 Patented Nov. 5, 1940 UNITED STATES su'rom'rro 'rELErnoNE SYSTEM Nils Emil Nilsson, Stockholm, Sweden, assignor to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden Application September 27, 1937, Serial No. 166,003 In Sweden September 28, 1936 iClaim.

The present invention relates to automatic telephone systems, and relates more particularly to automatic telephone systems of the kind comprising a plurality oi' groups oi' private branch 1, extensions which cooperate with an automatic main exchange.

In such systems the switching devices appertaining to a group of private branch extensions have hitherto been disposed near the telephone l.) sets of the group, for example in the business house in which the extension stations of the group are located, and have been combined to form a so called private automatic branch exchange or P. A. B. X. exchange which is connected to the selectors oi' the automatic main exchange over one or more main lines, the telephone connections between the various telephone sets or extension stations within such P. A. B, X. exchange being established over local selectors provided within the exchange, or in the business house or other locality housing the telephone sets.

The present invention has for its object to provide a more economic disposition o! the switching devices appertaining to a group of private branch extensions. According to the invention this object is substantially attained by connecting one or moretelephone sets belonging to a group of extension stations directly to banks oi contacts of final selectors appertaining to the 3l) system oi' the main exchange, and by extending the subscribers lines for the other telephone sets of said group of extension stations directly to an auxiliary exchange or group exchange which is common to a number of groups of extension stations, connecting said subscribers lines in said group exchange to switches serving to establish connections not only between the telephone sets belonging to said groups of extension stations but also between said telephone sets and the tele- 4f, phone sets of the ordinary subscribers belonging to the main exchange. Such a disposition of the lines and switching devices oi' the several groups of extension stations will make the subscribers lines longer and more expensive, it is true, than when disposing the switching devices in the hitherto known manner, but said additional cost will be small, particularly for large main exchanges serving several groups of extension stations, in comparison with the savings obtained-due to the reduction in maintenance costs and in the reduction in the number of selectors and relay sets for call-back connections entailed when combining the switching devices of several groups of extension stations in the manner proposed by the invention.

`in similar mann-er as the groups AI-A3.

The invention will now be described more in detail with reference to the accompanying drawing which shows an example of the application of the invention.A

In an automatic main exchange are provided 5 call nders Si group selectors GVI and GV2 and iinal selectors LVI. The iinal selectors LVI, which in the illustrated embodiment serve exclusively i'or establishing telephone connections with groups oi private branch extensions, for exl0 ample with a business house equipped with a number of extension stations, can be connected over a line selector S2 t0 9. group selector GV2. The telephone sets oi a group of private branch extensions are designated AI-A3. 0f said sets 15 the set Al, which is used by an operator, is connected directly to the bank oi contacts of the iinal selector LVI., whereas the other telephone sets or extension stations A2 and A3 are connected directly to the bank oi' contacts of line 20 selectors S4 and selectors LV2 and LV3 which are provided exclusively for establishing telephone connections with the various telephone sets appertainlng to the respective groups of private branch extensions and which are combined 25 according to the invention to form a separate auxiliary or group exchange which cooperates with the main exchange. Consequently, the group of extension stationsA to which the telephone sets AI-A3 belong, will have no individual 30 selectors in that other groups of extension stations will be connected to the group exchange The manner of operation oi the system will be clear from the following description oi' the switching 35 operations taking place when establishing a telephone connection.

When an ordinary subscriber appertaining to the automatic main exchange intends to make a call and lifts of! his microtelephone he will be 40 connected over aline selector Si to a free register Rei which stores the desired number. The register thereafter controls the setting of the group selectors GVI and GV2 and of the nal selector.

If the call is intended for an ordinary subscriber 45 belonging to the main exchange, the group selector GV2 will hunt in known manner for a junction line which extends directly to a final selector to the contact eld of which the desired subscriber is connected. Said iinal selector will 50 then be set in ordinary manner, whereafter the connection is completed.

If, on the other hand, the subscribers number stored in the register belongs to the groups of extension stations in question, the group selector GV2 will be set on a link line LI which is connected with the bank of contacts of a line selector S2 the wipers of which are connected over a link line L2 to a final selector LVI.

The line selector S2 is set in ordinary manner on the calling line LI. The iinal selector LVI will then be set in accordance with the stored number on a line ALI which extends to an ordinary telephone set AI attended by an operator. The calling subscriber now informs the operator at AI of the desired number or of the name of the desired subscriber belonging to the group of extension stations in question. The operator thereafter connects herself or himself to the desired subscriber, for example A2 in the following manner. The subscriber transmits by means of his or her dial a current impulse which impulse in known manner actuates a relay set associated with the link line LI. Thereby a throwover contact VI is operated in such a way that the link line LI is connected over a line L3 to a selector S3 which in usual way starts to hunt for the calling line L3, connecting the same to a free cord line L5 and at the same time connecting a free register Re2 to the circuit. The selector S3 is provided in known manner, as indicated on the drawing, with double wipers one of which is connected upon a call to aline L3 and the other one connected at the same timeto a line L4 which extends directly to the line LI. At the call the test relay of the selector operates a contact K, however, so that only the line L3 will be connected into circuit. The operator thereafter dials the number of the desired extension station, the connection being then extended under control of the register Re2 to the line AL2 over a nal selector LV2 appertaining to the line L5. When thereafter the operator replaces her microtelephone the throw-over the switch VI and the contact device K will be eiective anew in a known manner. The calling subscriber will then, as soon as the subscriber A2 has answered, become automatically connected with the extension station A2 over the contact device K now shifted back to its position of rest, the selector S3, the

link line Ll extending between the bank of contacts of the selector and the line LI, and the contact device VI. After said transfer of connections the selector S2 as well as the final selector LVI will be free and both of them can be taken ln use for establishing other connections.

Upon a call from a subscriber within the group of P. A. B. X. subscribers AI-A3, for instance the subscriber A3, a selector Sl willl be started, said selector then connecting the line AL3 with a cord line L6 and a free register Re3. The register receives the current impulses sent from the subscriber and, provided that the call is intended for instance for a subscriber A2 appertaining to the same group of subscribers, the register will set a final selector LV3 on the desired line AL2. If the call is intended for an ordinary subscriber connected to the main exchange the nal selector LV3 will be set on a junction line L1 which is connected in ordinary manner over a switching device V2 to the bank ofcontacts of a call nder of the main exchange, for example the call finder SI, and the telephone connection will then be completed over said call finder in the previously described manner. Since the junction line L'I is very much utilized it may be desirable to connect the same directly to a register and to a Junction line connected with a group selector GVI as indicated on the drawing with the dotted line L3.

On establishing such a connection from the group exchange to the main exchange a call-back connection can be established through the intermedium of a circuit shitting device V2 in that when the subscriber A3 after the establishing of a connection dials a current impulse, for instance,

the device'V2 will be shifted in known manner and the call effected over a selector S3.

In the drawing are shown only three extension stations in the group but a group of extension stations can, of course, have every desired size.' Furthermore, each group of extension stations can be equipped with more than one operators telephone, the additional connecting devices being then connected to the bank of contacts of the final selector in the same manner as the telephone set AI. A certain group of extension stations can thus have several numbers in the bank of contacts of the iinal selector LVI and of the other final selectors connected in multiple therewith. It is also possible to connect the operators Atelephone or other telephones within the same group of extension stations both to the bank of contacts of the iinal selector LVI and to the bank of contacts of the switches S4, LV2, LV3, common to several groups of extension stations. Every other group of extension stations can be connected up in similar manner as the illustrated group AI-A3.

I claim:

In a telephone system, group selectors and iinal selectors in an automatic main exchange, junction lines between said selectors, line selectors for connecting said final selectors to the junction lines extending to said group selectors, a plurality of groups of extension stations which cooperate with the automatic main exchange, at least one telephone set Vbelonging to a group of extension stations connected directly to banks of contacts of the final selectors appertaining to the system of the main exchange, the subscriber lines for the other telephone sets belonging to said group of extension stations extending directly to an auxiliary exchange which is common to a number of groups of extension stations, switches in said auxiliary exchange serving to establish connections between the telephone sets belonging to said groups of extension stations and also between said telephone sets and the telephone sets of the ordinary subscribers belonging to the main exchange, circuit shifting devices provided in said junction lines between group selectors and final selectors of the main exchange, whereby call-back connections from the telephone sets connected directly to the nal selectors are established over said circuit shifting devices and over switches in the auxiliary exchange to telephone sets connected to the auxiliary exchange, and means for disconnecting the final selector and the line selector from the circuit after the establishment of a call-back connection over said junction lines as soon as the circuit is transferred to another telephone set belonging to the auxiliary exchange.

NlLS EMIL NILSSON. 

